Column for liquid and gas chromatography

ABSTRACT

Column for carrying out gas or liquid chromatography comprising several capillaries coupled in parallel the capillaries being arranged side by side or woven or pleated together in the form of a flat band-like device, whereby the column can be bent and rolled up without tensions arising in same.

The present invention relates to a column for performing liquid and gaschromatography, particularly the latter, comprising a plurality ofcapillaries coupled in parallel.

Gas chromatography based on the use of single capillaries as a column isoften used to a large extent in analytic chemistry. The differentadvantages and effects which can be obtained by such capillary columnsare extensively described in the literature, for example Kaiser, R. E.:Chromatographie in der Gasphase, third ed., Vol. 2, BibliographischesInstitut, Mannheim, 1975; Ettre, L. S.: Open Tubular Columns in GasChromatography, Plenum Press, New York, 1965.

The primary advantage of using a capillary column is the good separationeffect that can be obtained. Thus, it is generally known that thesmaller the interior diameter of the column the better the dissolution,i.e. the separation of the components of the gas mixture. However,capillary columns are subject to the obvious disadvantage that theircapacity is strongly delimited, which necessitates the use of particularsample injecting devices and very sensitive detectors.

The use of several capillary columns with as identical properties aspossible and coupled in parallel could result in elimination of thedisadvantage residing in the limited capacity of the capillary column.By using a larger number of capillary columns coupled in parallel itwould thus be possible to separate and prepare substances in a pure formin larger quantities while maintaining the ability of the singlecapillary column of chromatographic dissolution.

However, hitherto proposed multicapillary column constructions have notbeen found to be practically useful, mainly in view of the fact that ithas been found to be difficult to provide for a column composed ofseveral capillaries coupled in parallel wherein in practical operationthe individual capillaries show a somewhat identically similarbehaviour. The differences that may arise between the individualcapillaries in the composite column can consist in deformation of thecapillaries in different degrees depending on the position in the columnstructure, arising temperature gradients over the cross section of thecolumn, etc. The first one of said differences between the individualcapillaries in the column can be wholly devastating for the operationalcharacteristic in view of the fact that the linear flow through acapillary tube is proportional to the fourth power of the inner diameterof the tube in accordance with Poiseuille's equation: (modified)

    F=(πd.sup.4 ·dp)/(128ηdL)

wherein

d=tube diameter

dp=pressure differential

η=gas viscosity

L=length of tube

F=gas flow (ml/min.)

For longer tubes having a greater pressure drop also the compressibilityof the gas must be introduced as a factor but this does not change thedependence of the gas flow of the fourth power of the diameter.

Another essential disadvantage of proposed constructions based on themulti-capillary column is the relatively large thermal mass of thecolumn, whereby it is not possible rapidly to change the temperature ofthe column without causing radial temperature gradients which result indifferent separation rates of the different capillaries which results inloss of the dissolution ability of the multicolumn.

The present invention has for its purpose to provide a column forcarrying out gas chromatography and wholly or partly avoiding the abovedisadvantages. For this object the invention provides for a columnwherein the capillaries are arranged side by side or woven or pleatedtogether in the form of a flat band-like device. By arranging the columnin this manner the essential advantages are obtained residing in thefact that the column can be bent and rolled up without resultingtensions and deformations in same.

In its simplest form the column according to the present inventionconsists of capillaries arranged side by side, the capillariespreferably in some suitable manner being held together mechanically, atleast laterally. The simplest way of keeping the capillaries togetherconsists in baking same into some suitable binding material, for examplea hardenable plastic.

In an alternative embodiment of the column according to the inventionthe capillaries are held side by side by gluing to a support, forexample a plastic foil, or are arranged between two layers of forexample plastic and are fixed by gluing to the two layers.

In the column according to the invention the capillaries may also beanchored mechanically in another manner, for example by lateral threadsarranged in zigzag in relation to the capillaries. It is alsopractically fully conceivable to provide for mechanical anchorage of thecapillaries to each other by weaving or pleating the individualcapillaries together to form a flat woven or pleated product.

At both ends of the column according to the invention the capillariesare manifolded in a suitable manner for supply of carrier gas forchromatography and for discharge of separated products. In this case itis suitable, at least at one end of the column, to leave the capillariesfree and separate from each other over a part of their lengths to enabletrimming, which is further explained below, and to facilitatemanifolding the capillaries to a unit.

A suitable capillary tube material is a flexible strong material andpreferably silica capillaries are used which can be made with very thinwalls and with a very small cross section diameter, down to about 0.1 mmor even less. In order to impart the necessary mechanical strength tothe silica capillaries it is suitable to coat same with a thin layer ofpolymer, for example silicon or polyimide or of metal. An alternativeconceivable material for the manufacture of the capillary tubes is steelor other metal or glass.

Assuming that flexibility can be maintained a few flat band-like devicescan be positioned on top of each other, but an upper limit would seem toexist at 3-4 capillary layers arranged on top of each other. No upperlimit as how many capillaries can be arranged side by side exists, sincethe column can be given any width with maintained flexibility and thusmaintained uniform capillary characteristic. Since with today'stechniques silica capillaries can be made which have a very smalldiameter, one may easily prepare a multi-capillary column containing 100capillaries laterally arranged and with a lateral dimension of less than5 cm.

In the following the invention will be described by examples ofembodiments in connection with the appended drawings, wherein:

FIG. 1 shows diagrammatically one end of a column according to theinvention;

FIG. 2 shows a cross-section taken along line II--II in FIG. 1 and inenlargement;

FIG. 3 shows a cross-section through an alternative embodiment;

FIG. 4 shows a cross-section through yet another embodiment of thecolumn of the invention;

FIG. 5 shows another modified embodiment of the column of the invention;and

FIG. 6 shows diagrammatically a device for rolling up the column of theinvention to the formation of a compact unit.

In FIG. 1 there is shown diagrammatically a column made in accordancewith the present invention and generally designated 1. The column isbuilt up by capillaries 3 arranged side by side which capillaries at theends thereof are baked together to a unit contained in a protectingsleeve 5.

In FIG. 2 there is shown a cross-section through the column taken alongline II--II in FIG. 1, from which it is clear that the individualcapillaries 3 are positioned side by side somewhat separated and gluedto a support 7, for example a plastic film. The capillaries 3 extendbeyond said plastic film 7 a distance which is clear from FIG. 1 for apurpose to be further explained below.

In FIG. 3 there is shown a modified embodiment wherein the capillaries 3are arranged side by side immediately adjacent to each other and bakedinto a plastic mass 9. Baking in of the capillaries in a polymer can bedone by feeding capillary tubes from individual spools through a bath ofa non-cured polymer. As a starting material there may be used anysuitable curing plastic, for example polyimide or silicon, and the bandobtained which is not yet cured can be passed through an oven whereinpolymerization takes place, the band being wound onto a drum until thedesired length has been obtained.

In FIG. 4 there is shown a cross-section through yet another alternativeembodiment of the column of the invention. In this embodimentcapillaries 3 are arranged on a central support 11, for example plasticfoil, on either sides either loosely positioned on the foil or fixedthereto by for example gluing, there being obtained a two-layer columnwith maintained good flexibility.

In FIG. 5 is shown a cross-section through an embodiment of the columnof the invention, wherein the individual capillaries 3 are anchoredmechanically side by side through lateral thread elements 13, forexample of metal, plastic or other suitable material. The embodimentaccording to FIG. 5 can be said to be a woven product, wherein thecapillaries 3 constitute the warp and thread elements 13 the weft.

It is also conceivable mechanically to attach the capillaries inrelation to each other by some kind of plaiting, whereby it suitably isprovided for the plait obtained being so flat that its thickness doesnot exceed a dimension corresponding to 2 to 3 capillary diameters.

FIG. 6 shows a device enabling winding up a long column so as to obtainit in a compact form. For gas chromatographic applications sometimes alength of column of up to about 200 meters may be desirable, and suchcolumn will, of course, in its extended form be clumsy to handle.However, the column construction in accordance with the inventionenables assembling the column within a relatively small volume, such asillustrated in FIG. 6, with maintained low heat inertia.

In FIG. 6 the column 1 according to the invention is arranged wound upin the shape of a helix in a diagrammatically shown housing 15containing guide pins 17 for arranging column 1 in a wound up formaccording to the figure. The outer left end is manifolded in the samemanner as shown in FIG. 1 within a protecting sleeve 5, whereas theopposite end of column 1 in the centre of the helix is divided up intotwo parts 1a, 1b which, outside the casing 15, are brought together inanother protecting sleeve 5.

Even while one using modern techniques could obtain capillary tubes witha very close tolerance with regard to its inner diameter it is, however,in view of Poiseuille's equation as referred to above essential to becapable of trimming the column with regard to the individualcapillaries. Such trimming can be carried out before or after theinterior coating of the capillary tubes with a stationary phase. If thetrimming takes place before coating with stationary phase the flowresistance of the different tubes is suitably investigated by pressing aliquid, for example dichloromethane, into the capillaries andregistering the positions of the liquid columns in the differentcapillaries immediately before leaving same. After thus establishing thepositions in the tubes corresponding to the same effective column lengththe tubes can be severed at the positions marked and the ends levelledtogether while using the above mentioned free part of the capillaries.

Trimming of the capillaries can be performed also after coating withstationary phase. In this case each capillary is tested with regard toits chromatographic retention properties and adjustment in length can becalculated with Poiseuille's equation and the retention value obtained.Testing can be performed with for example a hydrocarbon, such as octaneor nonane, at room temperature.

After the trimming procedure the ends of the capillaries are broughttogether to a bundle and the protecting sleeve 5 is moved on to the endwhich may then be permanently fixed by using for example a curingplastic.

The column according to the instant invention has essential advantagesamong which the following may be mentioned.

The construction allows rapid heating (temperature programming) in viewof the small thermal mass in relation to exposed surface. Temperaturegradients between the capillaries can be avoided, which is necessary inorder that the dissolving ability of the individual capillaries shall bepractically utilized parallel and synchronously.

The construction allows maintained mechanical flexibility of the columnwhich can be wound up in the form of a spool without resulting inmechanical stresses so that the capillaries break or are mechanicallyreleased from each other.

When flexing the column in for example winding all capillaries in thecolumn will maintain the same length.

The invention is not delimited to the above embodiments but can bemodified in many respects within the scope of the appended patentclaims.

I claim:
 1. A gas or liquid chromatography column comprising a pluralityof capillary tubes coupled in parallel, the capillary tubes beingarranged in the form of a flat band-like device, allowing the column tobe bent and rolled up without tensions arising in same, the capillarytubes being adapted at a first end of the column to receive a supply ofcarrier fluid and at a second end of the column for discharge ofseparated products.
 2. The column of claim 1, wherein the capillarytubes are laterally held together mechanically.
 3. The column of claim2, wherein the capillary tubes are held together by baking same into abinding material.
 4. The column of claim 3, wherein the binding materialis a thermosetting resin.
 5. The column of claim 2, wherein thecapillary tubes are held together by being glued side by side onto asupport.
 6. The column of claim 5 wherein the support is a plastic foil.7. The column of claim 2, wherein the capillary tubes are held togetherby laterally extending threads.
 8. The column of claim 2, wherein thecapillary tubes are held together by weaving or pleating the individualcapillary tubes together.
 9. The column of claim 1, wherein thecapillary tubes at least at one end of the column, are left free overpart of their lengths to enable trimming and to facilitate manifoldingthe capillary tubes.
 10. The column of claim 1, wherein the capillarytubes are made of silica.
 11. The column of claim 10, wherein thecapillary tubes are coated on their exterior with a thin polymer ormetal layer.
 12. The column of claim 1, wherein the capillary tubes aremade from steel.
 13. The column of claim 1, wherein a plurality of flatband-like devices are positioned on top of each other.
 14. The column ofclaim 1, wherein the capillary tubes are arranged side by side.